水/岩相互作用对焦家金矿金成色的影响

The Effect of Water/Rock Interaction for the Gold Fineness of Jiaojia Gold Deposit

金成色对于金矿研究是一个重要的参数,其受到成矿流体的pH值和Na/(Na+K)等因素的影响。成矿过程的水/岩相互作用过程往往控制着这些物理化学参数。焦家金矿以强烈的水/岩相互作用为特征,并且由于其Ⅰ号矿体和Ⅲ号矿体的围岩不同,导致水/岩相互作用存在差异。本文研究聚焦于焦家金矿Ⅰ号矿体和Ⅲ号矿体不同的水/岩相互作用对金成色的影响。通过镜下矿石矿物组合显微观察确定出产于Ⅰ号矿体和Ⅲ号矿体中多金属硫化物阶段(第Ⅲ成矿阶段)的银金矿,并利用电子探针分析第Ⅲ成矿阶段银金矿以及进行围岩蚀变矿物对平衡热力学计算,对影响金成色的pH和Na/(Na+K)进行探究后认为:(1)焦家金矿Ⅰ号矿体和Ⅲ号矿体中第Ⅲ成矿阶段银金矿金成色相近;(2)水/岩相互作用过程中,成矿流体受黄铁绢英岩和钾长石化花岗岩缓冲后导致pH和Na/(Na+K)发生一定的变化,但这2种变化对金成色的影响不大。

The gold fineness is a very important parameter for the gold deposit research and it is affected by many factors such as pH value and Na/(Na+K)of the ore-forming fluid.The water/rock interaction between oreforming fluid and wall rock usually controls those important physico-chemical parameters.Jiaojia gold deposit is characterized by the intense water/rock interaction.No.Ⅰand No.Ⅲorebodies in the Jiaojia gold deposit have different water/rock interaction due to different wall rocks.The study in this paper mainly focuses on the gold fineness comparison of the stageⅢmineralization(quartz-polymetallic sulfide stage)between No.Ⅰand No.Ⅲorebodies.The stageⅢgold in two orebodies has been distinguished under the microscope.They were analyzed by the EPMA and the gold fineness was calculated according to analysis results.The mineral equilibrium phase image was calculated to estimate the variation tendency of pH value and Na/(Na+K)of the ore-forming fluid.Two points could been known according to this study:(1)The gold fineness in the stage III mineralization between No.Ⅰand No.Ⅲis similar;(2)pH value and Na/(Na+K)could be different when the ore-forming fluid was buffered by the pyrite-sericite-quartz alterated rock and K-feldsparation rock,but this difference has a little effect on the gold fineness.